ELECTROCHEMICAL METHOD FOR HIGH-TEMPERATURE MOLTEN SALT ELECTROLYSIS IN HUMID ATMOSPHERE

Abstract

Disclosed is an electrochemical method for high-temperature molten salt electrolysis in humid atmosphere. The method involves preparing hydrogen gas, metals/alloys, metal oxide compounds and metal hydrides in humid high-temperature molten salt environment. Hydrogen gas is generated by electrolyzing water in a molten salt electrolyte at above 100 C., and with a working cathode being a solid-state oxide pellet and a voltage applied to the electrolyzing cell being far lower than that in a direct electro-deoxidation process, the hydrogen gas generated reduces solid-state oxide cathodes to produce metals. The hydrogen ions in the molten salt can be prepared by hydrolysis reaction of the molten salt in a water vapor containing atmosphere. Corresponding metals or alloys or metal oxide compounds can be prepared by reducing iron oxide, molybdenum oxide, tantalum oxide, nickel oxide, copper oxide, titanium oxide or corresponding compound oxides and the like.

Claims

1. A method of producing hydrogen by high-temperature molten salt electrolysis in humid atmosphere, wherein the method is conducted in a humid molten salt electrolysis environment, and the hydrogen is produced by the molten salt electrolysis; where the temperature of the molten salt is 150 to 1000 C., the water vapor content of the molten salt protective atmosphere is 0.1 to 100 Vol. %, and the molten salt electrolyte is one or more of LiF, LiCl, LiBr, LiI, NaF, NaCl, NaBr, NaI, KF, KCl, KBr , KI, RbF, RbCl, RbBr, RbI, CsF, CsCl, CsBr, CsI, MgCl.sub.2, MgF.sub.2, CaCl.sub.2,CaF.sub.2, SrCl.sub.2, SrF.sub.2, BaCl.sub.2, BaF.sub.2 and ZnCl.sub.2.

2. (canceled)

3. (canceled)

4. The method of producing hydrogen by high-temperature molten salt electrolysis in humid atmosphere according to claim 1, wherein in the method of producing hydrogen by high-temperature molten salts in humid atmosphere, during the molten salt electrolysis, the molten salt electrolyte contains HCl, HF or HL and the voltage of the molten salt electrolysis is 0.7 to 3V

5-10. (canceled)

11. A method for producing metals/alloys by high-temperature molten salt electrolysis in humid atmosphere, wherein the method is carried out in a humid molten salt electrolysis environment, solid metal oxide cathodes are reduced in-situ by hydrogen generated through the electrolysis in the molten salt, the metal oxides are used as working cathodes during the electrolysis, and corresponding metals/alloys are produced; among them, the temperature of the molten salt is 150 to 1000 C., the water vapor content of the protective atmosphere of the molten salt is 0.1 to 100 Vol. %, and the molten salt electrolyte is a mixture of one or more components of alkali metal halides and/or alkaline earth metal halides.

12. The method for producing metals/alloys by high-temperature molten salt electrolysis in humid atmosphere according to claim 11, wherein the metal oxide is a working cathode.

13. The method for producing metals/alloys by high-temperature molten salt electrolysis in humid atmosphere according to claim 11, wherein the metal oxide is placed in the molten salt electrolyte, the molten salt electrolyte dissolves hydrogen ions, and the temperature of the molten salt is 150 to 1000 C.

14. The method for producing metals/alloys by high-temperature molten salt electrolysis in humid atmosphere according to claim 11, wherein in the method for producing metals/alloys by high-temperature molten salts in humid atmosphere, the molten salt electrolyte is one or more of LiF, LiCl, LiBr, LiI, NaF, NaCl, NaBr, NaI, KF, KCl, KBr, KI, RbF, RbCl, RbBr, RbI, CsF, CsCl, CsBr, CsI, MgCl.sub.2, MgF.sub.2, CaCl.sub.2, CaF.sub.2, SrCl.sub.2, SrF.sub.2, BaCl.sub.2, BaF.sub.2 and ZnCl.sub.2.

15. The method for producing metals/alloys by high-temperature molten salt electrolysis in humid atmosphere according to claim 14, wherein the molten salt electrolyte is LiCl.

16. (canceled)

17. (canceled)

18. The method for producing metals/alloys by high-temperature molten salt electrolysis in humid atmosphere according to claim 11, wherein the metal oxide is one or a mixture containing at least one of MoO.sub.3, WO.sub.3, PbO, CuO, ZnO, SnO.sub.2, V.sub.2O.sub.3, Cr.sub.2O.sub.3, CoO, NiO or Mn.sub.2O.sub.3.

19. The method for producing metals/alloys by high-temperature molten salt electrolysis in humid atmosphere according to claim 18, wherein the voltage of the molten salt electrolysis is 2V.

20. The method for producing metals/alloys by high-temperature molten salt electrolysis in humid atmosphere according to claim 11, wherein the metal oxide is one or a mixture containing at least one of TiO.sub.2, ZrO.sub.2, UO.sub.2, SiO.sub.2, or Nb.sub.2O.sub.5.

21. The method for producing metals/alloys by high-temperature molten salt electrolysis in humid atmosphere according to claim 20, wherein the voltage of the molten salt electrolysis is 3V.

22. The method for producing metals/alloys by high-temperature molten salt electrolysis in humid atmosphere according to claim 11, wherein the voltage of the molten salt electrolysis is 1 V, the metal oxide is Fe.sub.2O.sub.3 and the electrolysis product is metallic iron.

23. The method for producing metals/alloys by high-temperature molten salt electrolysis in humid atmosphere according to claim 11, wherein during the molten salt electrolysis, the molten salt electrolyte contains HCl, HF or HI.

24. The method for producing metals/alloys by high-temperature molten salt electrolysis in humid atmosphere according to claim 11, wherein hydrogen ions in the molten salt electrolyte are derived from hydrolysis reaction of the molten salt under the humid atmosphere.

25. The method for producing metals/alloys by high-temperature molten salt electrolysis in humid atmosphere according to claim 11, wherein the temperature of the water vapor brought into the molten salt electrolysis reactor is 100 C.

26. The method for producing metals/alloys by high-temperature molten salt electrolysis in humid atmosphere according to claim 11, wherein the temperature of the molten salt is greater than or equal to the melting temperature of the molten salt +1 C.; and the heating rate of the molten salt is 0.1 to 100 C./min.

27. (canceled)

28. The method for producing metals/alloys by high-temperature molten salt electrolysis in humid atmosphere according to claim 11, wherein the molten salt electrolysis voltage is 0.7 to 3V.

29. A method of producing metal oxide compounds by high-temperature molten salts in humid atmosphere, wherein the method is carried out in a humid molten salt electrolysis environment, solid metal oxide cathodes are reduced in-situ by hydrogen generated through electrolysis in the molten salt, during the electrolysis, the metal oxides are used as working cathodes, and corresponding metal oxide compounds are prepared; among them, the temperature of the molten salt is 150 to 1000 C., the water vapor content of the protective atmosphere of the molten salt is 0.1 to 100 Vol. %, and the molten salt electrolyte is one or more of LiF, LiCl, LiBr, LiI, NaF, NaCl, NaBr, NaI, KF, KCl, KBr, KI, RbF, RbCl, RbBr, RbI, CsF, CsCl, CsBr, CsI, MgCl.sub.2, MgF.sub.2, CaCl.sub.2, CaF.sub.2, SrCl.sub.2, SrF.sub.2, BaCl.sub.2, BaF.sub.2 and ZnCl.sub.2.

30. The method of producing metal oxide compounds by high-temperature molten salts in humid atmosphere according to claim 29, wherein in the method of producing metal oxide compounds by high-temperature molten salts in humid atmosphere, the metal oxide is one or a mixture containing at least one of MoO.sub.3, WO.sub.3, PbO, CuO, ZnO, SnO.sub.2, V.sub.2O.sub.3, Cr.sub.2O.sub.3, CoO, NiO, Mn.sub.2O.sub.3, TiO.sub.2, ZrO.sub.2, UO.sub.2, SiO.sub.2 or Nb.sub.2O.sub.5, and the metal oxide is the working cathode and a certain cathode polarization potential is applied.

31.-33. (canceled)

34. The method of producing metal oxide compounds by high-temperature molten salts in humid atmosphere according to claim 29, wherein during the molten salt electrolysis, the molten salt electrolyte contains HCl, HF or HI.

35.-39. (canceled)

40. The method of producing metal oxide compounds by high-temperature molten salts in humid atmosphere according to claim 29, wherein the molten salt electrolysis voltage is 0.7 to 3V.

41.-60. (canceled)

61. The electrochemical method of high-temperature molten salt electrolysis in humid atmosphere according to claim 1, wherein the product prepared by the method contains one or more of metallic compounds TiAl, Ti.sub.3Al, NiAl, TiAl.sub.3, NiAl.sub.3, NbAl, Nb.sub.3Al, FeAl, Fe.sub.3Al and CoAl.

62. The method of producing metal oxide compounds by high-temperature molten salts in humid atmosphere according to claim 18, wherein the electrolysis product is Li.sub.2Fe.sub.3O.sub.5.

63. The method according to claim 1, wherein in the humid molten salt electrolysis environment, solid metals are use as the cathode, and the metals are hydrogenated by the hydrogen generated by the molten salt electrolysis, and the corresponding metal hydrides are produced.

Description

DESCRIPTION OF THE DRAWINGS

[0084] FIG. 1 shows the electrochemical device for high-temperature molten salt electrolysis in humid atmosphere used in Examples 1 to 3 of the present invention;

[0085] FIG. 2 shows the electrochemical device for high-temperature molten salt electrolysis in humid atmosphere used in Examples 4 to 6 of the present invention;

[0086] FIG. 3 shows XRD patterns of the products prepared in Examples 1 to 3 of the present invention;

[0087] FIG. 4 shows the scanning electron micrograph of the prepared metal oxide compound prepared in Example 1 of the present invention;

[0088] FIG. 5 shows the scanning electron micrograph and EDX spectrum of the metal oxide compound prepared in Example 3 of the present invention;

[0089] FIG. 6 shows XRD patterns of the initial materials and products prepared in Example 8 of the present invention.

[0090] FIG. 7 shows the XRD analysis of the product produced in Example 10 of the present invention.

[0091] As disclosed within Figures, 1 is molten salt reactor for preparing hydrogen, 2 is quartz protective sleeve, 3 is graphite crucible, 4 is molten salt electrolyte, 5 is working cathode, 6 is cathode lead rod, 7 is inert gas bottle, 8 is gas guide pipe, 9 is container, 10 is water, 11 is anode lead rod, 12 is steam generating device, 13 is gas inlet, 14 is separator duct, 15 is chiller, 16 is water outlet, 17 is hydrogen, and 18 is quartz cover.

DETAILED DESCRIPTION

[0092] The characterization and analysis equipment used comprised of X-ray diffractometer (XRD, MPDDY2094, copper target, wavelength 1.5405 , Panakko, Netherlands), scanning electron microscope (SEM, Ultra Plus, Zeiss, Germany) equipped with energy dispersive spectrometer (EDS, Shimadzu Corporation), and infrared carbon sulfur analyzer (CS230, American LECO company). The electrolysis experiments were conducted using a constant voltage and constant current power supply (IT6502D, ITECH), and the current-time relationship during the electrolysis process was recorded. A molybdenum wire was used as the reference electrode, and the anodic potential and cathodic potential during the electrolysis process were recorded by a multimeter (Keysight 34460A). A hydrogen sensor was used to monitor and record the hydrogen concentration of the escaping gas during the electrolysis experiment.

[0093] The electrochemical device for high-temperature molten salt electrolysis in humid atmosphere, explained in Examples 1 to 3, is used for the preparation of metals/alloys/metal oxide compounds/metal hydrides. As shown in FIG. 1, the molten salt reactor for preparing hydrogen 1 comprises a retort made of stainless steel or Inconel alloy. The retort has a quartz protective sleeve 2 and a quartz cover 18 to prevent corrosion of the stainless steel retort by high-temperature molten salt; at the bottom of the quartz sleeve, there is a graphite crucible 3 used as the electrolysis reaction vessel, the crucible contains molten salt electrolyte 4, such as LiCl, CaCl.sub.2, MgCl.sub.2 and NaCl, or a mixed molten salt thereof; metal oxide is inserted into the molten salt electrolyte and used as the working cathode 5, the working cathode 5 can be made of metal oxide powder which is compression molded and sintered at a suitable temperature to make the working cathode 5 with suitable structural strength. The working cathode 5 is wound around one end of the cathode lead rod 6 using a high-melting metallic wire and the cathode lead rod 6 is sheathed by an alumina ceramic protection tube. During the electrolysis process, the water is brought into the reactor through an inert gas (argon or nitrogen); the gas in the inert gas bottle 7 flows into the container 9 containing deionized water through the gas guide pipe 8, and then the humidified gas flows into the molten salt reactor for preparing hydrogen 1. The container 9 may be made of glass, and the water vapor brought into the reactor can be dissolved in the molten salt 4, and the molten salt is hydrolysed to generate hydrogen ions; 11 is a metal lead rod connected to the graphite crucible. During the electrolysis process, the cathode lead rod 6 is connected to the negative pole of the power supply; the anode lead rod 11 is connected to the positive pole of the power supply, and 12 is the outlet pipe for the protective gas in the reactor.

[0094] According to Examples 4 to 6, the electrochemical device for high-temperature molten salt electrolysis in humid atmosphere is used to prepare metals/alloys/metal oxide compounds/metal hydrides. As shown in FIG. 2, the molten salt reactor for preparing hydrogen comprises of a retort made of stainless steel or Inconel alloy. The molten salt reactor for preparing hydrogen 1 can be sealed; the molten salt reactor for preparing hydrogen 1 has a quartz protective sleeve 2 and a quartz cover 18 to prevent the corrosion of the stainless steel retort from high-temperature molten salt. The graphite crucible 3 which is a container for the electrolysis reaction is located at the bottom of the quartz casing. The graphite crucible is filled with molten salt electrolyte 4, such as LiCl, CaCl.sub.2, MgCl.sub.2 and NaCl, or their mixed molten salts. Before the start of the electrolysis process, the temperature is raised to a certain temperature according to the established procedure, so that the molten salt is completely melted. A working electrode 5 made of metallic molybdenum or tungsten with mesh shape is located inside the graphite crucible. Working cathodes can also be made of ceramic materials, such as LiTiO.sub.2, which have a certain conductivity and sufficient thermal shock resistance. The working cathode is connected to the cathode lead rod 6. During the electrolysis process, the steam generating device 12 continuously injects water vapor through the gas guide pipe 8 into the reactor. The water vapor brought into the reactor can dissolve in the molten salt electrolyte 4, and the molten salt is hydrolysed to form hydrogen ions. 11 is a metallic anode lead rod connected to the graphite crucible. During the electrolysis process, the cathode lead rod 6 is connected to the negative pole of a power supply, and the anode lead rod 11 is connected to the positive pole of the power supply. Under a cathode polarization potential, hydrogen ions dissolved in molten salt are discharged at the cathode to produce hydrogen. The hydrogen/water vapor mixture generated by the electrolytic process escapes the reactor through the separator duct 14, entering chiller 15. At a temperature below 25 C., the water vapor in the mixture is liquefied and collected by the outlet pipe 16, and then recycled. The hydrogen escaped from the process is dried, collected and stored.

Example 1

[0095] Presented is a method of preparing metal oxide by high temperature molten salt electrolysis in humid atmosphere, using the electrochemical device shown FIG. 1, in which a pressed porous iron oxide pellet (20 mm in diameter and 3 mm in thickness) is the working cathode, and the pellet is wrapped and fixed on a copper lead rod (800 mm in length and 6 mm in diameter, covered by a corundum protection tube) using nickel wire. A high-purity graphite crucible (55 mm in inner diameter 55 mm, 15 mm in wall thickness, and 140 mm in height) containing 250 g anhydrous LiCl is used. A molybdenum wire with the diameter of 1 mm and length of 800 mm is employed as the reference electrode.

[0096] The electrolytic cell is heated to 660 C. at a heating rate of 5 C. per minute, the electrolysis temperature is higher than the melting point of LiCl molten salt by about 50 C., and the water vapor content of the molten salt protective atmosphere is 0.75 Vol. %. The electrolysis voltage is 1V and the electrolysis time is 1 h. During the electrolysis process, the flow rate of argon gas into the electrolysis cell was 600 mL/min. A U-shaped quartz tube was filled with deionized water. After the argon gas flowed through the U-shaped quartz tube, the humid argon gas flowed into the sealed reactor. After the electrolysis experiment is completed, and cooling down to room temperature, the salt present in the graphite crucible was washed with deionized water, and the cathode pellet was eventually retrieved. The separated cathode pellet was thoroughly washed with deionized water to remove residual salt and dried in a vacuum drying oven.

[0097] The XRD pattern of the product is shown in FIG. 3. After electrolysis at 1V for 1 h, the phase composition of the product is Li.sub.2Fe.sub.3O.sub.5. The SEM micrograph of the product (FIG. 4) shows that the micro-morphology of the product obtained is in the form of uniform octahedral structures with a particle size of 1 to 5 m.

Example 2

[0098] Presented is a method of preparing metals by high temperature molten salt electrolysis in humid atmosphere, according to the electrochemical device and parameter conditions described in Example 1, with the exception that the electrolysis time is 5 h and the water vapor content in the molten salt protective atmosphere is 0.8 Vol. % . The XRD pattern of the product is shown in FIG. 3. As can be seen from FIG. 3, the phase composition of the product consists of Li.sub.2Fe.sub.3O.sub.5 and Fe. The diffraction peaks at 2=44.7 and 82.4 correspond to the metallic iron phase. The results show that iron oxide can be reduced to metallic iron at a voltage lower than its theoretical decomposition voltage.

Example 3

[0099] Presented is a method of preparing metals by high temperature molten salt electrolysis in humid atmosphere, according to the electrochemical device described in Example 1, with the exception that the electrolysis voltage is 1.4 V, the electrolysis time is 5 h, and the water vapor content of the molten salt protective atmosphere is 1.0 Vol. %. The XRD pattern of the product is shown in FIG. 3. From the XRD analysis results presented in FIG. 3, it can be seen that the product obtained by the electrolysis process is metallic iron. The scanning electron micrograph and the EDX energy spectrum of the product are shown in FIG. 5. The EDX energy spectrum result corresponds to the white square marked area in the scanning electron micrograph. The SEM and EDS results further show that the iron oxide is completely reduced to metallic iron, and the particle size of the product does not exceed 10 m. The carbon content of the electrolytic product is about 0.3 wt %.

Example 4

[0100] Presented is a method of producing hydrogen by high temperature molten salt electrolysis in humid atmosphere using the electrochemical device shown in FIG. 2, in which the molten salt electrolyte is LiCl, the electrolysis temperature is 650 C., and the water vapor content of the molten salt protective atmosphere is 0.75 Vol. %. The working cathode is an iron rod, and the electrolysis voltage is 0.9V. The gas product obtained by electrolysis is hydrogen, which is detected by a hydrogen sensor.

Example 5

[0101] Presented is a method of producing hydrogen by high temperature molten salt electrolysis in humid atmosphere using the electrochemical device shown in FIG. 2, in which the molten salt electrolyte is LiCl, the electrolysis temperature is 650 C., and the water vapor content of the molten salt protective atmosphere is 0.8 Vol. %. The working cathode is tungsten mesh, the electrolysis voltage is 1V, and the gas product obtained by electrolysis is hydrogen, which is detected by a hydrogen sensor.

Example 6

[0102] Presented is a method of producing hydrogen by high temperature molten salt electrolysis in humid atmosphere using the electrochemical device shown in FIG. 2, in which, the molten salt electrolyte is LiCl, the electrolysis temperature is 650 C., and the water vapor content of the molten salt protective atmosphere is 0.9 Vol. %. The working cathode is nickel mesh, and the electrolysis voltage is 1.4 V. The gas product obtained by the electrolysis process is hydrogen, which is detected by a hydrogen sensor.

Example 7

[0103] Presented is a method of producing hydrogen by high temperature molten salt electrolysis in humid atmosphere using the electrochemical device shown in FIG. 2, in which the molten salt electrolyte is LiCl, the electrolysis temperature is 650 C., and the water vapor content of the molten salt protective atmosphere is 1.0 Vol. %. The working cathode is a LiTiO.sub.2 ceramic pellet, and the electrolysis voltage is 2V. The gas product obtained by the electrolysis process is hydrogen, which is detected by a hydrogen sensor.

Example 8

[0104] Presented is a method of preparing metals by high-temperature molten salt electrolysis in humid atmosphere. The high-temperature molten salt electrolysis method for preparing a high-temperature molten salt humid atmosphere uses the electrochemical device of Example 1, and the difference from Example 1 are that: the working cathode raw material is cobalt oxide (Co.sub.3O.sub.4), the electrolysis voltage is 0.97 V, the electrolysis time is 6 h, and the water vapor content in the molten salt protection atmosphere is 1.0 Vol. %. The XRD pattern of the initial material and the product are shown in FIG. 6. As can be seen from the XRD analysis of FIG. 6, the electrolytic product is metallic cobalt phase.

Example 9

[0105] Presented is a method of preparing metals by high-temperature molten salt electrolysis in humid atmosphere, in which the humid atmosphere of high-temperature molten salt is prepared by high-temperature molten salt electrolysis method using the electrochemical device explained in Example 1. Differences with Example 1 are: the working cathode material is nickel oxide (NiO), the electrolytic voltage is 0.97 V, the electrolytic time is 6 h, and the water vapor content in the molten salt protection atmosphere is 1.0 Vol. %. The XRD pattern of the product identified the electrolytic product to be metallic nickel phase.

Example 10

[0106] Presented is a method of preparing metals by high-temperature molten salt electrolysis in humid atmosphere, in which the humid atmosphere of high-temperature molten salt is prepared by high-temperature molten salt electrolysis method using the electrochemical device explained in Example 1. Differences with Example 1 are: the raw material (5) is a mixture of TiO.sub.2 (75 wt %) and Al.sub.2O.sub.3 (25 wt %), the electrolysis voltage is 2.8V, the electrolysis time is 9 h, the water vapor content in the molten salt protection atmosphere is 2 Vol. %, and the working temperature is 770 C. FIG. 7 shows the XRD pattern of the product. As can be seen, the product is a mixture of intermetallic phases Ti.sub.3Al and TiAl.

Example 11

[0107] Presented is a method of preparing metals by high-temperature molten salt electrolysis in humid atmosphere, in which the humid atmosphere of high-temperature molten salt is prepared by high-temperature molten salt electrolysis method using the electrochemical device explained in Example 1. Differences with Example 1 are: the raw material (5) is TiO.sub.2, the electrolysis voltage is 2.8V, the electrolysis time is 15 h, the water vapor content of the molten salt atmosphere is 2 Vol. %, the molten salt is LiCl-10 wt % KCl, and the operating temperature is 770 C. The product was metallic titanium.